Method and apparatus for centrifugally plating



METHOD AND APPARATUS FOR CBNTHIFUGALLY PLATING Filed Dec. 8. 1965 Sept. 2, 1969 (5. w. MATTSON 4 Sheets-Sheet 1 Sept. 2, 1969 e. w. MATTSON 4 Sheets-Sheet 2 Filed Dec.

FIG.

Filed Dec, 8, 1965 p 2, 1959 s. w. MATTSON 3,464,846

METHOD AND APPARATUS FOR CENTRIFUGALLY PLATING 4 Sheets-Sheet 5 Sept. 2, 1969 Filed Dec. 8'; 1 965 G. W. MATTSON METHOD AND APPARATUS FOR CENTRIFUGALLY PLATING 4 Sheets-Sheet 4 FIG. 4

United States Patent 3,464,846 METHOD AND APPARATUS FOR CENTRIFUGALLY PLATING George W. Mattson, Baton Rouge, La., assignor to lilthyl Corporation, New York, N.Y., a corporation of Virginia Filed Dec. 8, 1965, Ser. No. 512,478 Int. Cl. C23c 13/02, 17/00 US. Cl. 117107.1 5 Claims ABSTRACT OF THE DISCLOSURE Prior art techniques of vapor plating small parts have had numerous disadvantages. Such techniques have been unduly laborious and time consuming, still without achieving uniform coatings. As a consequence, due to the excess of labor and high number of rejected defectively coated parts, expense has been prohibitive. Additionally, waste of vapor plating compound in prior art methods and apparatus has been excessive. It is an object of the present invention to overcome each of these disadvantages.

Broadly, the present invention is drawn to a method and apparatus for centrifugally vapor plating small parts such as rivets, bolts, screws, pins, nuts, etc. In prior art techniques, such parts have been individually secured in holding devices prior to vapor plating. This is tedious, time consuming work and involves an amount of labor frequently disproportionate to the valueof the coating. And further, the part is not coated on the area in which it is secured to a holding device. The present invention overcomes both of these disadvantages. First, the parts are not secured to holding devices; they are simply dumped randomly into a basket or bowl. Second, there is thus no securing area on the parts which is masked from coating; hence, the parts may be uniformly completely coated.

Specifically, the method of the present invention consists of randomly placing parts in a bowl or basket which may or may not be perforate (hereinafter referred to as containers). The parts may be piled up without harm to the process, but such pile should be preferably far from completely filling the container. To a limited degree, the fewer the parts, the easier it is to achieve uniform coatings. This will become more apparent as explained hereinafter. Once the parts have been thus located, the container is rotated, at first slowly. Simultaneously, plating vapor is introduced into the container. As the r.p.m. of the container increases, the parts begin to spread out into a single layer thickness and climb up the sides of the container. The rotation of the container and parts causes the vapor to form an adjacent contiguous layer of almost uniform thickness. If the container is imperforate, this layer moves up the sides and over the edges thereof. Meanwhile, the vapor is contacting each of the parts which is also being forced by centrifugal force to crawl up the sides of the bowl. Such parts generally are rotating or tumbling, each upon its own axis, as each crawls up the sides of the bowl. Hence, the flowing vapor is contacting all sides of each part and depositing a uniform metal coating thereon. This sequence is repeated,

Patented Sept. 2, 1969 only in reverse, as the r.p.m. is decreased and the parts tumble back to the bottom of the bowl.

If the container is, on the other hand, perforate, the vapor is pulled by vacuum directly through the basket. And, as the parts are forced centrifugally to tumble up and then down the sides of the basket, each part has all its area exposed to the vapor and receives a relatively uniform coating thereover.

It is evident that the fewer the parts, the less coating is rubbed 01f each part by abrasive action between the parts.

Less vapor plating compound is wasted in the present invention because the ratio of area being coated to volume of coating vapor is maximized.

Other objects and features of the present invention will now in part be obvious and will in part appear hereinafter.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed disclosure taken in connection with the accompanying drawings wherein:

FIGS. 1 and 2 are a first embodiment of the invention.

FIG. 1 is a perspective view of the entire apparatus with a partial cutaway showing the interior of the vacuum box and a second partial cutaway showing the interior of the centrifugal bowl plater.

FIG. 2 is a cross-section on the line 2-2 of FIG. 1.

FIGS. 3 and 4 are a second embodiment of the invention.

FIG. 3 is a perspective view of the entire apparatus with a partial cutaway showing the interior of the vacuum box and a second partial cutaway showing the interior of the perforate centrifugal bowl plater.

FIG. 4 is a cross-section on the line 44 of FIG. 3.

FIGS. 1 and 2 show the first of two embodiments of the invention. A centrifugal bowl 4 is located directly above a drive motor 9, the connection therebetween being a drive axle 5. Motor 9 is of a reversible and variaable speed type. This apparatus is located within a cylindrical chamber which is separated into two sections by wall 10. The upper section is vacuum box 3 and contains the centrifugal bowl plater. The lower section is motor box 12 and contains motor 9. Wall 10 forms a tight fit with axle 5 as it is necessary to keep excessive amounts of vapor plating compound away from the motor. A vacuum is pulled on vacuum box 3 by vacuum means (not shown) through feed exhaust 2. The vacuum has two purposes: first, it removes oxygen and water vapor which cause defective coatings, and second, it removes unused and decomposed vapor plating compound. Centrifugal bowl 4, having an overhanging lip 11, is covered with heating elements 6 over which is insulation layer 7. Parts-to-be-coated 8 are within bowl 4. Feed pipe 1 extends concentrically into bowl 4 but does not touch the bowl bottom or the parts-to-be-coated.

In the operation of this first embodiment parts-to-becoated 8 are placed randomly inside the centrifugal bowl plater 4. The temperature of the bowl and parts is elevated by means of heating elements 6; heat is conserved with insulation layer 7. Simultaneously, the atmosphere within vacuum box 3 is evacuated through feed exhaust 2. Once a proper temperature is reached, vapor plating compound is introduced via feed port 1. At this same time, rotation of the centrifugal bowl is begun with variable speed motor 9. The randomly placed parts in the bowl begin to spread out due to centrifugal force. As the r.p.m. increases, the parts are forced up the sides of the bowl. Meanwhile, of course, vapor plating compound is striking the parts on the bottom of the bowl, moving up the sides of the bowl and over the parts thereon in a contiguous layer and eventually, around the top edges of the bowl. As the vapor moves up the sides of the bowl,

it is contacting the heated parts and pyrolytically decomposing to form a uniform thin metal coating upon each part. All sides of each part are coated since each part is forced to tumble or roll in moving up the sides of the centrifugal bowl plater. The bowl has an overhanging edge or lip 11 which prevents parts from being inadvertently forced out of the bowl. This same operation is repeated, only in reverse, when the r.p.m. of the bowl is decreased and the parts tumble or roll back to the bottom of the bowl. Once the layer of vapor plating compound has passed around the top edges of the bowl, it is pulled by vacuum down to feed exhaust port 2 and exhausted.

It is to be noted that the present apparatus is unlike a tumbling basket wherein coated parts have their coatings chipped and worn by abrasion caused by the continual falling and rubbing of the parts. A principal advantage of the present apparatus is that tumbling of the parts is gentle because of the centrifugal force tending to hold the parts against the wall and because there is no jerky start to rotation of the bowl.

It is evident that numerous changes may be made without departing from the scope of this embodiment. For example, the bowl may be rotated by means located above or beside it; vapor plating compound may be refluxed; the bowl need not be spherical but may be numerous other shapes including semicylindrical; rotation need not be imparted to the bowl along its centerline but may be offset therefrom.

FIGS. 3 and 4 show a second embodiment of the invention. In this second embodiment vapor moves through a perforate bowl rather than around the top edges of an imperforate bowl. Element 103 is an electrically heated perforate centrifugal bowl plater which is connected to a variable speed motor 106 by drive axle 107. Both bowl and motor are located within a chamber which is divided into two sections by wall 108. The upper section is vacuum box 105 and contains perforate bowl 103. The lower section, motor box 110, contains motor 106 and shields it from vapor plating compound. Bowl 103 contains parts-to-be-coated 102 and has an inwardly overhanging lip 109. Metal plating compound is fed in through entry port 101. Vapor plating compound and other gases remaining after the coating process are exhausted by vacuum means (not shown) through exhaust port 104.

The operation of this embodiment is not unlike that of the first embodiment. In fact, the only difference is in the direction of vapor flow. Here, flow is directly through the bowl rather than around the edges of the bowl or both through and around the bowl. This embodiment is especially advantageous in coating intricate parts having interior surfaces difficult to reach by the vapor flow of the first embodiment. Vapor flow takes both a lateral direction as in the first embodiment and a direction through and between the parts as it flows through the perforate container.

It is evident that the apparatus of each of the above embodiments may be of widely varied sizes. For example, the bowl may vary from less than 6 inches to more than 6 feet. The rate of rotation of the bowl is manifestly dependent upon the size, shape and density of the parts and upon the size of the bowl and can vary over a wide range, for example, from 10 to 500 r.p.m. for parts of a certain size. It is further apparent that numerous different vapor plating compounds may be used with the present invention which are well known and fully described in the art. For example, metals to be deposited may be introduced as gaseous metal carbonyls, organometallic plating compounds, or vaporized solutions of certain of the metal carbonyls or organometallics in readily vaporizable solvents. For many applications it is desired to produce an aluminum coating upon the substrate parts and this may be accomplished by using organoaluminum compounds, e.g. aluminum alkyls such as triethylaluminum, triisobutylaluminum and the like. However, a preferred aluminum coating compound is trimethylam'inealane which may be utilized to coat at temperatures ranging from to 350 C. The magnitude of the vacuum pulling the plating vapor through the apparatus is of course dependent upon the desired flow rate of vapor, the properties of the plating compound being employed, and the like. Optimum flow rates may be readily determined experimentally on the basis of information already available in the literature.

I claim as my invention:

1. A method for depositing a metal coating upon parts comprising:

(a) depositing the parts in the bottom of a bowlshaped container;

(b) rotating the container and thereby gently spreading the parts up the sides of said container;

(c) directing a vapor plating compound into the container and upon the parts;

(d) pyrolytically decomposing the vapor plating compound when in contact with the parts so as to deposit a metal coating thereon; and

(e) ceasing rotation of said container, thereby allowing said parts to gently return to said bottom.

2. The method of claim 1 wherein the container is perforate and the vapor plating compound is directed into and through said perforate container.

3. An apparatus for depositing a metal coating upon parts comprising:

(a) a bowl-shaped container for holding the parts;

(b) means to rotate the container and thereby roll said parts out of the bottom and up the inner side of the bowl;

(0) means to prevent said ports from rolling out of said container; and

((1) means to direct vapor plating compound into the container and into contact with the parts.

4. The apparatus of claim 3 wherein said container is perforate.

'5. The apparatus of claim 3 wherein the preventing means is an inwardly overhanging lip on the top edge of said container.

References Cited UNITED STATES PATENTS 3,017,854 11/1962 OBrien 118-303 3,187,715 6/1965 Wellard 117-1071 X 3,213,827 1'0/1965 Jenkin 11849.5 3,220,875 11/1965 Queneau 117l07.l X 3,307,515 3/1967 Wiener et al 11848 X FOREIGN PATENTS 967,682 8/1964 Great Britain.

ALFRED L. LEAVITT, Primary Examiner A. GOLIAN, Assistant Examiner US. Cl. X.R. 

